Noland T A, Kuo J F
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
J Biol Chem. 1991 Mar 15;266(8):4974-8.
Effects of troponin phosphorylation on Ca2(+)-stimulated MgATPase activity of bovine cardiac actomyosin were examined. Phosphorylation by protein kinase C of troponin I and troponin T subunits in troponin or troponin-tropomyosin complex resulted in a decreased Ca2(+)-stimulated MgATPase activity in reconstituted actomyosin, and this effect was reversed by subsequent dephosphorylation by protein phosphatase 1. It was further observed that protein kinase C phosphorylation of either troponin I or troponin T subunits led to a similar inhibition of Ca2(+)-stimulated actomyosin MgATPase activity. In all cases, EC50 values (concentrations causing 50% stimulation) for Ca2+ were not appreciably affected by troponin phosphorylation by protein kinase C. Data from phosphorylation site analysis suggests that phosphorylation of threonine 144 in troponin I and possibly threonine 280 or threonine 199 in troponin T might be important for the observed decrease of Ca2(+)-stimulated actomyosin MgATPase. It is suggested that inhibition of actomyosin MgATPase caused by protein kinase C phosphorylation of troponin I and/or troponin T represents a new mechanism that can account for in part the reported negative inotropic effect of phorbol esters on various cardiac preparations.
研究了肌钙蛋白磷酸化对牛心肌肌动球蛋白Ca2(+)-刺激的MgATP酶活性的影响。肌钙蛋白或肌钙蛋白-原肌球蛋白复合物中肌钙蛋白I和肌钙蛋白T亚基经蛋白激酶C磷酸化后，重组肌动球蛋白中Ca2(+)-刺激的MgATP酶活性降低，随后经蛋白磷酸酶1去磷酸化可逆转此效应。进一步观察到，肌钙蛋白I或肌钙蛋白T亚基经蛋白激酶C磷酸化均导致对Ca2(+)-刺激的肌动球蛋白MgATP酶活性产生类似的抑制作用。在所有情况下，蛋白激酶C对肌钙蛋白的磷酸化均未明显影响Ca2+的EC50值（引起50%刺激的浓度）。磷酸化位点分析数据表明，肌钙蛋白I中苏氨酸144的磷酸化以及肌钙蛋白T中可能的苏氨酸280或苏氨酸199的磷酸化对于观察到的Ca2(+)-刺激的肌动球蛋白MgATP酶活性降低可能很重要。提示蛋白激酶C对肌钙蛋白I和/或肌钙蛋白T的磷酸化所引起的肌动球蛋白MgATP酶抑制代表一种新机制，这可以部分解释佛波酯对各种心脏制剂所报道的负性肌力作用。
